Processing biomass

ABSTRACT

Biomass feedstocks (e.g., plant biomass, animal biomass, and municipal waste biomass) are processed to produce useful products, such as fuels. For example, systems are described that can convert feedstock materials to a sugar solution, which can then be fermented to produce a product such as a biofuel.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/491,797 filed Jun. 8, 2012, which claims thebenefit of U.S. Provisional Application No. 61/495,217 filed Jun. 9,2011. The complete disclosure of these applications is herebyincorporated by reference herein.

BACKGROUND

Cellulosic and lignocellulosic materials are produced, processed, andused in large quantities in a number of applications. Often suchmaterials are used once, and then discarded as waste, or are simplyconsidered to be waste materials, e.g., sewage, bagasse, sawdust, andstover.

SUMMARY

Processes are disclosed herein for saccharifying or liquifying a biomassmaterial, e.g., cellulosic, lignocellulosic and/or starchy feedstocks,by converting biomass material to low molecular weight sugars, e.g.,saccharifying the feedstock using an enzyme, e.g., one or more cellulaseand/or amylase. The invention also relates to converting a feedstock toa product, e.g., by bioprocessing, such as fermentation. The processesinclude wet milling a feedstock. The inventors have found that wetmilling the feedstock tends to reduce the time required forsaccharification, and increase the concentration of sugar that can beobtained in a given saccharification time. Wet milling alone or workingsynergistically with any treatment described herein can reducerecalcitrance of a biomass material.

The processes disclosed herein can utilize low bulk density materials,for example cellulosic or lignocellulosic feedstocks that have beenphysically pretreated to have a bulk density of less than about 0.75g/cm³, e.g., less than about 0.7, 0.65, 0.60, 0.50, 0.35, 0.25, 0.20,0.15, 0.10, 0.05. or less, e.g., less than 0.025 g/cm³.

Such materials can be difficult to disperse in liquids, e.g., with wateror a solvent system for saccharification, fermentation, or otherprocessing. Due to their low bulk density, the materials tend to floaton the surface of the liquid rather than being wetted out and dispersedinto the liquid. In some cases, the materials can be hydrophobic, highlycrystalline, or otherwise difficult to wet. At the same time, it isdesirable to process the feedstock in a relatively high solids leveldispersion, in order to obtain a high final concentration of sugar inthe saccharified material, or a high concentration of the desiredproduct after processing (e.g., of ethanol or other alcohol(s) afterfermentation). In some cases, utilizing the methods described herein thesolids level of the dispersion during processing can be, for example, atleast 10, 15, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or even at least 50percent by weight dissolved solids. For example, the solids level can befrom about 10 to 50%, e.g., about 10-40%, 10-30%, or 10-20%.

In one aspect, the invention features reducing the particle size of alignocellulosic material to less than 3000 μm, e.g. less than 2000 μm,less than 1000 μm or even less than 500 μm, e.g., less than 250 μm orless than 100 μm. The particle size range can be between 100-3000 μm,e.g., 200-2000 μm, 200-1000 μm, 500-1000 μm.

In one aspect, the invention features reducing recalcitrance of alignocellulosic material and wet milling the lignocellulosic material.In some cases, recalcitrance is reduced prior to wet milling. Thematerial can be densified prior to reducing the recalcitrance or afterreducing the recalcitrance and prior to wet milling the material.

In another aspect, the invention features a method comprising wetmilling a lignocellulosic material, e.g., a lignocellulosic materialhaving a reduced recalcitrance.

Either of these aspects of the invention can include, in someimplementations, any of the following features.

The recalcitrance of the biomass material, e.g., a lignocellulosicmaterial, can be reduced, for example, by irradiating thelignocellulosic material, e.g., by exposing the material to an electronbeam. In some cases, irradiating comprises delivering a dose of at least5 Mrad to the lignocellulosic material, e.g., at least 10, 20, 30, 50,100, 150 or even 200 Mrad. For example, doses can be in the range of5-200 Mrad, e.g., 5-100 Mrad, 5-50 Mrad, 5-10 Mrad, 10-100 Mrad, or10-50 Mrad.

The lignocellulosic material may be, for example, a material is selectedfrom the group consisting of wood, particle board, sawdust, agriculturalwaste, sewage, silage, grasses, rice hulls, bagasse, cotton, jute, hemp,flax, bamboo, sisal, abaca, straw, wheat straw, corn cobs, corn stover,switchgrass, alfalfa, hay, coconut hair, seaweed, algae, and mixturesthereof.

The biomass may also be combinations of starchy, lignocellulosic and/orcellulosic materials. For example, a biomass can be an entire plant orpart(s) of a plant e.g., a wheat plant, cotton plant, a corn plant, riceplant or a tree.

In some implementations, wet milling is performed using a rotor/statorhead. The rotor and stator may include nesting rings of teeth. In somecases, the stator comprises two or more concentric rings of teeth, andthe rotor comprises a ring of teeth configured to fit between adjacentrings of teeth of the stator. The clearance between the rotor and statoris generally small, to generate high shear, and may be, for example fromabout 0.01 to 0.25 inches (0.25 to 6.4 mm). The spacing between theteeth in each ring of teeth is also generally small, e.g., from about0.1 to 0.3 inch (2.5 to 7.6 mm).

Wet milling may be performed using a plurality of rotor/stator heads,e.g., when the process is performed in a large tank or vessel.

Wet milling is generally performed at a relatively high shear rate. Theshear rate may be, for example, at least 20,000 sec⁻¹, (e.g., at least25,000 sec⁻¹, at least 30,000 sec⁻¹, at least 40,000 sec⁻¹ or at least50,000 sec⁻¹). The shear rate can be, for example from about 30,000sec⁻¹ to about 50,000 sec⁻¹ (e.g., from about 25,000 sec⁻¹ to about50,000 sec⁻¹, from about 30,000 sec⁻¹ to about 50,000 sec⁻¹, from about35,000 sec⁻¹ to about 50,000 sec⁻¹, from about 40,000 sec⁻¹ to about50,000 sec⁻¹, from about 20,000 sec⁻¹ to about 45,000 sec⁻¹, from about20,000 sec⁻¹ to about 40,000 sec⁻¹, from about 20,000 sec⁻¹ to about30,000 sec⁻¹, from about 30,000 sec⁻¹ to about 40,000 sec⁻¹).

In some implementations, wet milling is performed in-line. A jet mixermay be applied during wet milling. The jet mixer may also be used duringsubsequent processing, e.g., during fermentation. The method may furtherinclude adding an enzyme to the biomass material, e.g., alignocellulosic material, before, during or after wet milling, and/oradding a microorganism to the biomass material or a sugar derived fromthe biomass material. In some cases, the microorganism is added afterwet milling has been completed, e.g., to avoid damage to themicroorganism from wet milling. In some implementations, themicroorganism converts the biomass feedstock or sugar to a productselected from the group consisting of alcohols, organic acids, sugars,hydrocarbons, and mixtures thereof.

The methods described herein generally provide relatively rapid andeffective processing of a relatively high solids level of feedstock. Byincreasing the initial solids level of feedstock in the mixture, theprocess can proceed more rapidly, more efficiently and morecost-effectively, and a high resulting concentration can generally beachieved in the final product. In some cases, solids may be removedduring saccharification, e.g., by a centrifuge, and more feedstock maybe added. The removed solids may be used as a product, e.g., as acombustible fuel for cogeneration of electricity and/or as an animalfeed.

The saccharification processes described herein allow biomass material,e.g., a cellulosic or lignocellulosic feedstock, to be converted to aconvenient and concentrated form which can be easily transported andutilized in another manufacturing facility, e.g., a facility configuredto ferment sugar solutions to alcohols, to manufacture a product, e.g.,a fuel such as ethanol, butanol or a hydrocarbon. Such concentrates canuse less water, which can result in substantial manufacturing andtransportation cost savings.

Some processes disclosed herein include saccharification of thefeedstock, and transportation of the feedstock from a remote location,e.g., where the feedstock is produced or stored, to the manufacturingfacility. In some cases, saccharification can take place partially orentirely during transport.

In some cases, the systems described herein, or components thereof, maybe portable, so that the system can be transported (e.g., by rail,truck, or marine vessel) from one location to another. Such mobileprocessing is described in U.S. Ser. No. 12/374,549 filed Jan. 21, 2009and International Application No. WO 2008/011598, the full disclosuresof which are incorporated herein by reference.

Exemplary products that can be produced by employing the methodsdescribed herein include hydrocarbons, proteins, alcohols (e.g., amonohydric alcohols or a dihydric alcohols), such as ethanol,isobutanol, n-propanol or n-butanol, carboxylic acids, such as aceticacid, lactic acid, citric acid, propionic acid, succinic acid,3-hydroxyproprionic acid or butyric acid, salts of a carboxylic acid, amixture of carboxylic acids and salts of carboxylic acids and esters ofcarboxylic acids (e.g., methyl, ethyl and n-propyl esters), ketones,aldehydes, alpha unsaturated acids, beta unsaturated acids, such asacrylic acid, olefins, such as ethylene, butenes, and mixtures of any ofthese. Specific examples include ethanol, propanol, propylene glycol,butanol, 1,4-butanediol, 1,3-propanediol, methyl or ethyl esters of anyof these alcohols, methyl acrylate, methylmethacrylate, Products alsoinclude sugars, e.g., glucose, xylose and xylitol. These and otherproducts are described in U.S. Ser. No. 12/417,900 filed Apr. 3, 2009;the full disclosure of which is incorporated by reference herein.

In one aspect, the invention features a wet milling system comprising awet mill disposed in a fluid having a biomass material dispersedtherein. The system can, for example, be used for processinglingocellulosic material that has optionally been irradiated (e.g., withan electron beam). The system can include a jet mixer disposed in thefluid. The wet milling systems can include a rotor/stator head, forexample with the rotor and stator including nesting rings of teeth.Furthermore, the stator can have two or more concentric rings of teeth.Other aspects of the invention include a tank with one or more jet head,and one or more wet mill disposed in the tank.

Bulk density is determined using ASTM D1895B. Briefly, the methodinvolves filling a measuring cylinder of known volume with a sample andobtaining a weight of the sample. The bulk density is calculated bydividing the weight of the sample in grams by the known volume of thecylinder in cubic centimeters.

All publications, patent applications, patents, and other referencesmentioned herein or attached hereto are incorporated by reference intheir entirety for all that they contain.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the enzymatic hydrolysis of celluloseto glucose.

FIG. 2 is a flow diagram illustrating conversion of a feedstock tosugars and other products. FIG. 2A is a diagrammatic illustration of asaccharification system according to one embodiment. FIG. 2B is adiagrammatic illustration of a saccharification system according toanother embodiment.

FIG. 3 is a schematic diagram of an ethanol manufacturing facility thathas been retrofitted to utilize the solutions and suspensions disclosedherein.

FIG. 4 is a top plan view of the assembled rotor and stator of a wetmilling head according to one embodiment. FIG. 4A is an enlarged sectionview of FIG. 4 showing the clearance between the rotor and stator.

FIG. 5 is a perspective view of the rotor and stator together.

FIG. 6 is an exploded perspective of the rotor and stator.

FIG. 7 is a bottom plan view of the rotor taken along view line 7-7 ofFIG. 6.

FIG. 8 is a top plan view of the stator taken along view line 8-8 ofFIG. 6.

FIG. 9 is an enlarged view of the area of the rotor indicated in FIG. 7.

FIG. 10 is an enlarged view of the area of the stator indicated in FIG.8.

FIG. 11 is a top plan view of the assembled rotor and stator of a wetmilling head according to a second embodiment. FIG. 11A is an enlargedsection view of FIG. 11 showing the clearance between the rotor andstator.

FIG. 12 is a perspective view of the rotor and stator together.

FIG. 13 is an exploded perspective of the rotor and stator.

FIG. 14 is a bottom plan view of the rotor taken along view line 14-14of FIG. 13.

FIG. 15 is a top plan view of the stator taken along view line 15-15 ofFIG. 13.

FIG. 16 is an enlarged view of the area of the rotor indicated in FIG.14.

FIG. 17 is an enlarged view of the area of the stator indicated in FIG.15.

FIGS. 18 and 18A are diagrams illustrating jet flow exiting a jet mixernozzle.

FIG. 19 is a diagrammatic perspective view of a jet-flow agitatoraccording to one embodiment. FIG. 19A is an enlarged perspective view ofthe impeller and jet tube of the jet-flow agitator of FIG. 19. FIG. 19Bis an enlarged perspective view of an alternate impeller.

FIG. 20 is a cross-sectional view of a system for wet milling.

DETAILED DESCRIPTION

Using the methods described herein, biomass (e.g., plant biomass, animalbiomass, paper, and municipal waste biomass) can be processed to produceuseful intermediates and products such as organic acids, salts oforganic acids, anhydrides, esters of organic acids and fuels, e.g.,fuels for internal combustion engines or feedstocks for fuel cells.Systems and processes are described herein that can use as feedstockcellulosic and/or lignocellulosic materials that are readily available,but often can be difficult to process, e.g., municipal waste streams andwaste paper streams, such as streams that include newspaper, kraftpaper, corrugated paper or mixtures of these.

Generally, if required, materials can be physically treated forprocessing and/or after processing, often by size reduction. Many of theprocesses described herein can effectively lower the recalcitrance levelof the feedstock, making it easier to process, such as by bioprocessing(e.g., with any microorganism described herein, such as a homoacetogenor a heteroacetogen, and/or any enzyme described herein), thermalprocessing (e.g., gasification or pyrolysis) or chemical methods (e.g.,acid hydrolysis or oxidation). Biomass feedstock can be treated orprocessed using one or more of any of the methods described herein, suchas mechanical treatment, chemical treatment, radiation, sonication,oxidation, pyrolysis or steam explosion. The various treatment systemsand methods can be used in combinations of two, three, or even four ormore of these technologies or others described herein and elsewhere. Insome instances wet milling alone can reduce recalcitrance or actsynergistically or with other treatment processes described herein.

The processes disclosed herein can utilize low bulk density materials,for example cellulosic or lignocellulosic feedstocks that have beenphysically pretreated to have a bulk density of less than about 0.75g/cm³, e.g., less than about 0.7, 0.65, 0.60, 0.50, 0.35, 0.25, 0.20,0.15, 0.10, 0.05. or less, e.g., less than 0.025 g/cm³. Bulk density isdetermined using ASTM D1895B. Briefly, the method involves filling ameasuring cylinder of known volume with a sample and obtaining a weightof the sample. The bulk density is calculated by dividing the weight ofthe sample in grams by the known volume of the cylinder in cubiccentimeters. If desired, low bulk density materials can be densified,for example, by methods described in U.S. Pat. No. 7,971,809 the fulldisclosure of which is hereby incorporated by reference.

Saccharification

In order to convert the feedstock to a form that can be readilyprocessed, the glucan- or xylan-containing cellulose in the feedstock ishydrolyzed to low molecular weight carbohydrates, such as sugars, by asaccharifying agent, e.g., an enzyme or acid, a process referred to assaccharification. The low molecular weight carbohydrates can then beused, for example, in an existing manufacturing plant, such as a singlecell protein plant, an enzyme manufacturing plant, or a fuel plant,e.g., an ethanol manufacturing facility.

The feedstock is combined with the saccharifying agent in a liquidmedium, e.g., a solvent such as an aqueous solution, and the mixture iswet milled. Methods for wet milling the material in the liquid mediumare discussed in detail below. In some implementations, during and/orafter wet milling the saccharifying agent, material and liquid mediumare mixed using a jet mixer. In some cases jet mixing continuesthroughout saccharification.

In some implementations, the material and/or the saccharifying agent areadded incrementally rather than all at once. For example, a portion ofthe material can be added to the liquid medium, dispersed therein, andmixed with the saccharifying agent until the material is at leastpartially saccharified, at which point a second portion of the materialis dispersed in the medium and added to the mixture. This process cancontinue until a desired sugar concentration is obtained.

The feedstock can be hydrolyzed using an enzyme, such as a cellulase oran amylase or mixtures of these enzymes. For example, the biomassmaterial can be combined with the enzyme in a solvent, e.g., in anaqueous solution.

Enzymes and biomass-destroying organisms that break down biomass, suchas the cellulose and/or the lignin portions of the biomass, contain ormanufacture various cellulolytic enzymes (cellulases), ligninases orvarious small molecule biomass-destroying metabolites. These enzymes maybe a complex of enzymes that act synergistically to degrade crystallinecellulose or the lignin portions of biomass. Examples of cellulolyticenzymes include: endoglucanases, cellobiohydrolases, and cellobiases(β-glucosidases). Referring to FIG. 1, a cellulosic substrate isinitially hydrolyzed by endoglucanases at random locations producingoligomeric intermediates. These intermediates are then substrates forexo-splitting glucanases such as cellobiohydrolase to produce cellobiosefrom the ends of the cellulose polymer. Cellobiose is a water-soluble1,4-linked dimer of glucose. Finally cellobiase cleaves cellobiose toyield glucose. Suitable cellulases will be discussed herein in a latersection.

The time required for complete saccharification will depend on theprocess conditions and the feedstock and enzyme used. Ifsaccharification is performed in a manufacturing plant under controlledconditions, the cellulose may be substantially entirely converted toglucose in about 12-96 hours, e.g., less than 48 hour, less than 36hours, less than 24 hours, less than 18 hours, less than 12 hours oreven less than 8 hours. If saccharification is performed partially orcompletely in transit, saccharification may take longer.

In some cases, saccharification is performed at a pH of about 4 to 7,e.g., about 4.5 to 6, or about 5 to 6.

It is generally preferred that the final concentration of glucose in thesugar solution be relatively high, e.g., greater than 10 wt. %, orgreater than 15, 20, 30, 40, 50, 60, 70, 80, 90 or even greater than 95%by weight. This reduces the volume to be shipped, and also inhibitsmicrobial growth in the solution. After saccharification, the volume ofwater can be reduced, e.g., by evaporation or distillation.

A relatively high concentration solution can be obtained by limiting theamount of medium, e.g., water, added to the feedstock with the enzyme.The concentration can be controlled, e.g., by controlling how muchsaccharification takes place. For example, concentration can beincreased by adding more feedstock to the solution. In some cases,solids are removed during saccharification, e.g., by centrifuge,allowing more feedstock to be added. Solubility of the feedstock in themedium can be increased, for example, by increasing the temperature ofthe solution, and/or by adding a surfactant as will be discussed below.For example, the solution can be maintained at a temperature of 40-50°C., 50-60° C., 60-80° C., or even higher.

Fermentation

Microorganisms can produce a number of useful intermediates and productsby fermenting a low molecular weight sugar produced by saccharifying thetreated feedstock. For example, fermentation or other bioprocesses canproduce alcohols (e.g., n-butanol, isobutanol, ethanol or erythritol),organic acids (e.g., acetic, butyric, citric or lactic acid),hydrocarbons, hydrogen, proteins or mixtures of any of these materials.

Yeast and Zymomonas bacteria, for example, can be used for fermentationor conversion. Other microorganisms are discussed in the Materialssection, below. The optimum pH for fermentations is about pH 4 to 7. Theoptimum pH for yeast is from about pH 4 to 5, while the optimum pH forZymomonas is from about pH 5 to 6. Typical fermentation times are about24 to 168 (e.g., 24-96 hrs) hours with temperatures in the range of 20°C. to 40° C. (e.g., 26° C. to 40° C.), however thermophilicmicroorganisms prefer higher temperatures.

In some embodiments e.g., when anaerobic organisms are used, at least aportion of the fermentation is conducted in the absence of oxygen e.g.,under a blanket of an inert gas such as N₂, Ar, He, CO₂ or mixturesthereof. Additionally, the mixture may have a constant purge of an inertgas flowing through the tank during part of or all of the fermentation.In some cases, anaerobic conditions can be achieved or maintained bycarbon dioxide production during the fermentation and no additionalinert gas is needed.

In some embodiments, all or a portion of the fermentation process can beinterrupted before the low molecular weight sugar is completelyconverted to a product (e.g. ethanol). The intermediate fermentationproducts include high concentrations of sugar and carbohydrates. Thesugars and carbohydrates can be isolated as discussed below. Theseintermediate fermentation products can be used in preparation of foodfor human or animal consumption. Additionally or alternatively, theintermediate fermentation products can be ground to a fine particle sizein a stainless-steel laboratory mill to produce a flour-like substance.

The fermentations include the methods and products that are disclosed inU.S. Provisional Application Ser. No. 61/579,559, filed Dec. 22, 2011and U.S. Provisional Application Ser. No. 61/579,576, filed Dec. 22,2011 the disclosure of which is incorporated herein by reference.

Mobile fermenters can be utilized, as described in U.S. ProvisionalPatent Application Ser. No. 60/832,735, now Published InternationalApplication No. WO 2008/011598. Similarly, the saccharificationequipment can be mobile. Further, saccharification and/or fermentationmay be performed in part or entirely during transit.

Fuel Cells

Where the methods described herein produce a sugar solution orsuspension, this solution or suspension can subsequently be used in afuel cell. For example, fuel cells utilizing sugars derived fromcellulosic or lignocellulosic materials are disclosed in U.S.Provisional Application Ser. No. 61/579,568, filed Dec. 22, 2011, thecomplete disclosure of which is incorporated herein by reference.

Thermochemical Conversion

Thermochemical conversion can be performed on the treated feedstock toproduce one or more desired intermediates and/or products. Athermochemical conversion process includes changing molecular structuresof carbon-containing material at elevated temperatures. Specificexamples include gasification, pyrolysis, reformation, partial oxidationand mixtures of these (in any order).

Gasification converts carbon-containing materials into a synthesis gas(syngas), which can include methanol, carbon monoxide, carbon dioxideand hydrogen. Many microorganisms, such as acetogens or homoacetogensare capable of utilizing a syngas from the thermochemical conversion ofbiomass, to produce a product that includes an alcohol, a carboxylicacid, a salt of a carboxylic acid, a carboxylic acid ester or a mixtureof any of these. Gasification of biomass (e.g., cellulosic orlignocellulosic materials), can be accomplished by a variety oftechniques. For example, gasification can be accomplished utilizingstaged steam reformation with a fluidized-bed reactor in which thecarbonaceous material is first pyrolyzed in the absence of oxygen andthen the pyrolysis vapors are reformed to synthesis gas with steamproviding added hydrogen and oxygen. In such a technique, process heatcomes from burning char. Another technique utilizes a screw augerreactor in which moisture and oxygen are introduced at the pyrolysisstage and the process heat is generated from burning some of the gasproduced in the latter stage. Another technique utilizes entrained flowreformation in which both external steam and air are introduced in asingle-stage gasification reactor. In partial oxidation gasification,pure oxygen is utilized with no steam.

Systems for Treating a Feedstock

Referring to FIG. 2, a process for conversion of a feedstock to sugarsand other products, e.g., ethanol, can include, for example, optionallyphysically pre-treating the feedstock, e.g., to reduce its size (step110), before and/or after this treatment, optionally treating thefeedstock to reduce its recalcitrance (step 112), and saccharifying thefeedstock to form a sugar solution (step 114). Saccharification can beperformed by mixing a dispersion of the feedstock in a liquid medium,e.g., water with an enzyme (step 111), as will be discussed in detailbelow. During or after saccharification, the mixture (ifsaccharification is to be partially or completely performed en route) orsolution can be transported, e.g., by pipeline, railcar, truck or barge,to a manufacturing plant (step 116). At the plant, the solution can bebio-processed to produce a desired product, e.g., ethanol (step 118),which is then processed further, e.g., by distillation (step 120). Theindividual steps of this process will be described in detail below. Ifdesired, the steps of measuring lignin content (step 122) and setting oradjusting process parameters (step 124) can be performed at variousstages of the process, for example just prior to the process step(s)used to change the structure of the feedstock, as shown. If these stepsare included, the process parameters are adjusted to compensate forvariability in the lignin content of the feedstock, as described in U.S.application Ser. No. 12/704,519 filed in Feb. 11, 2010, the completedisclosure of which is incorporated herein by reference.

The mixing step 111 and saccharifying step 114 can be performed using,for example, either of the systems shown in FIGS. 2A and 2B. Thesesystems include a tank 136, which initially contains a liquid medium andlater contains a mixture 138 of liquid medium, feedstock andsaccharifying agent. The liquid medium is delivered to the tank througha valved piping system (not shown). The systems also include a hopper130, in communication with a dispersing unit 134. In the embodimentshown in FIG. 2B, the hopper 130 receives feedstock that has beentreated to reduce its size and optionally to reduce its recalcitrance(steps 110 and 112 above) by a feedstock pretreatment module 132. Inboth embodiments, the hopper may receive other dry ingredients, such asyeast and nutrients, e.g., from a supply 30. Optionally, a vibratingdevice 36 may be associated with the hopper, to facilitate delivery ofmaterial from the hopper. The system may also optionally include adispersing unit 134, e.g., if the feedstock is difficult to initiallywet with the liquid. The liquid medium is drawn into the dispersing unit134 from the tank, and returned to the tank by the dispersing unit viaan outlet pipe 137. The opening of outlet pipe 137 may be above theliquid level, as shown, or may in some instances be submerged in theliquid in the tank. In some cases, depending on the type of milling unitand dispersing unit used, the system may include a pump 139, e.g., apositive displacement pump, configured to circulate the liquid medium,and/or a viscometer 141 to monitor the viscosity of the dispersion andactivate the pump when the measured viscosity reaches a predeterminedvalue.

In the embodiment shown in FIG. 2A, the feedstock is delivered to thesurface of the liquid medium in the tank, e.g., via a delivery device 32having a delivery conduit 34 (e.g., hose or pipe). The delivery device32 may also be associated with a vibrating device 36, to facilitate flowof material into the device. The delivery device 32 may be, for example,a blower configured to blow fibrous and/or particulate material from asource to a location remote from the source through a hose, e.g., aninsulation blower such as the FORCE 3 blower available from Intec,Frederick, Colo. Alternatively, the material can be delivered to thesurface of the liquid using other techniques, such as gravity feed or ascrew conveyor.

In some implementations, the tank is provided with a flexible, airpermeable cover, or other device configured to allow air to vent fromthe tank during delivery of the feedstock, while preventing feedstockfrom blowing out of the tank and/or contaminants from entering the tank.

When the particles are generally spherical, e.g., as is the case withhammermilled corn cobs, or otherwise of a morphology that allows them tobe easily fed, the feedstock can be gravimetrically fed. For example,the feedstock can be delivered from a hopper above the tank.

As the feedstock material is delivered through delivery conduit 34 ontothe surface of the liquid in the tank, liquid is discharged throughoutlet pipe 137 of the dispersing unit 134 onto the material. Thedischarged liquid wets the feedstock material, causing it to sink intothe liquid, where it can be dispersed by the dispersing unit 134 (if oneis provided), optionally in combination with the mixing action of a jetmixer 144, discussed below.

Once the feedstock has been delivered to the tank, it is wet milled,using wet milling unit 160, which generally includes a high shearrotor/stator head. Examples of suitable milling units are described indetail below. The wet milling unit can be mounted in any desiredlocation in the tank. It can be side-mounted, as shown, or top andbottom mounted. In some implementations, the wet milling unit can beexternal to the tank and the tank contents can be pumped through the wetmilling unit and returned to the tank. In some cases, the wet millingunit is mounted adjacent to the jet mixing unit 144, described below. Insome cases, multiple wet milling heads are provided. For example, in alarge tank multiple wet milling heads may be mounted at spaced locationswithin the tank. Wet milling can be performed in-line or as a batchprocess.

Wet milling is generally performed at a high shear rate, for examplefrom about 20,000 sec⁻¹ to 60,000 sec⁻¹, or from about 30,000 sec⁻¹ to50,000 sec⁻¹.

The wet milling unit may be run for any desired length of time. The wetmilling unit can be run in a pulsed manner (e.g., the power to the motordriving the wet milling is pulsed), for example the shearing rate can bevaried periodically or non-periodically, or, as another example the wetmilling unit can be turned on an off repeatedly. Generally, wet millingis discontinued when either the efficiency of saccharification ceases tobe improved by wet milling (this can be determined by experimentationfor a given set of process parameters), or the shear generated by thewet milling unit causes the temperature of the tank contents to exceed apredetermined maximum value. The predetermined maximum value may be set,for example, based on the temperature at which the saccharifying agentwould be denatured in a short period of time.

Shearing can cause the mean particle size of the biomass material to bereduced. For example the size can be reduced from about more than 1 mm(e.g. more than 5 mm or more than 10 mm) to less than 1 mm (e.g., lessthan 0.5 mm, less than 0.1 mm or even less than 0.01 mm).

In some implementations, the wet milling unit can be used to heat, orpartially heat, the tank contents to a desired processing temperature.For example, in one implementation the tank contents are heated byanother means to approximately 40° C., and then the wet milling unit isoperated for a time sufficient to raise the temperature to approximately50° C., a temperature which is advantageous for saccharification. Insome cases, wet milling is performed for less than 8 hours, e.g., for 1to 4 hours or 1 to 2 hours. Wet milling may be performed for an evenshorter time, e.g., 30 minutes or less. Once this desired temperature isreached the wet milling device is turned off so as to prevent a furtherincrease in temperature. In some cases, the tank contents may be cooledduring or after wet milling to prevent overheating. In order to preventdenaturing of the enzymes used in saccharification, it is generallypreferred that the tank contents be maintained at or below 50° C., or atleast that temperature excursions above 50° C. be of sufficiently shortduration so as not to denature the enzymes.

Before, during, or after wet milling, a saccharifying agent is deliveredto the tank from a hopper 140, which includes a metering device 142.During saccharification, the contents of the tank are mixed, e.g., byone or more jet mixers. In some cases, the jet mixers are operatedduring wet milling. A jet mixer 144 is represented diagrammatically inFIGS. 2A and 2B; examples of suitable jet mixers will be described indetail below, and are also described in U.S. Ser. No. 12/782,694 filedMay 18, 2010; Ser. No. 13/293,985 filed Nov. 10, 2011; and Ser. No.13/293,977 filed Nov. 10, 2011 the full disclosures of which are herebyincorporated by reference herein. The jet mixer produces a jet using amotor 146 that drives a pump and/or a rotor (not shown). The torqueexerted by the motor 146 correlates with the solids level of the mixturein the tank, which in turn reflects the degree to which the mixture hassaccharified. The torque is measured by a torque monitor 148, whichsends a signal to a motor 150 that drives the conveyor 130 and also tothe metering device 142 of the hopper 140. Thus, the supply of thetreated feedstock and the enzyme can be interrupted and resumed as afunction of the saccharification of the contents of the tank. The datameasured by the torque monitor can also be used to adjust the jet mixer,e.g., to a lower RPM for a mixer that utilizes a rotor, or to a lowerjet velocity for a pump-driven mixer. Instead of, or in addition to, thetorque monitor, the system may include an Amp monitor (not shown) thatmeasures the full load amperage of the motor. In some cases, the jetmixer may include a variable frequency drive (VFD) to allow the speed ofthe motor to be adjusted.

The system may also include a heat monitor (not shown) that monitors thetemperature of the liquid medium and adjusts the feed rate of thefeedstock and/or the mixing conditions in response to increases intemperature. Such a temperature feedback loop can be used to prevent theliquid medium from reaching a temperature that will denature the enzyme.The heat monitor can also be used to determine when to shut off the wetmilling unit to avoid overheating of the tank contents.

When one or more pumps are used in the systems described herein, it isgenerally preferred that positive displacement (PD) pumps be used, e.g.,progressive cavity or screw-type PD pumps.

In some cases, the manufacturing plant can be, for example, an existinggrain-based or sugar-based ethanol plant or one that has beenretrofitted by removing or decommissioning the equipment upstream fromthe bio-processing system (which in a typical ethanol plant generallyincludes grain receiving equipment, a hammermill, a slurry mixer,cooking equipment and liquefaction equipment). Thus, the feedstockreceived by the plant is input directly into the fermentation equipment.A retrofitted plant is shown schematically in FIG. 3. The use of anexisting grain-based or sugar-based ethanol plant in this manner isdescribed in U.S. Ser. No. 12/704,521, filed Feb. 11, 2010, the fulldisclosure of which is incorporated herein by reference.

In some embodiments, rather than transporting the saccharified feedstock(sugar solution) to a separate manufacturing plant, or even a separatetank, the sugar solution is inoculated and fermented in the same tank orother vessel used for saccharification. Fermentation can be completed inthe same vessel, or can be started in this manner and then completedduring transport as discussed above. Saccharifying and fermenting in asingle tank are described in U.S. application Ser. No. 12/949,044, Nov.18, 2011, the full disclosure of which is incorporated herein byreference.

Generally, the oxygen level in the fermentation vessel should becontrolled, e.g., by monitoring the oxygen level and venting the tank,aerating (e.g., by mixing or sparging in oxygen or mixtures of gasescontaining oxygen) or de-aerating (e.g., by mixing in or sparging ininert gases such as nitrogen, carbon dioxide, helium and/or argon) themixture as necessary. In some cases, for example where anaerobicconditions are desirable as discussed previously, the rate of mixing iscritical. For example, at times during the process, no mixing may bedesirable so that gases produced during fermentation (e.g., CO₂, H₂ andor methane) can more effectively displace oxygen from the fermentationvessel. It is also desirable to monitor the level of ethanol in thevessel, so that when the ethanol level begins to drop the fermentationprocess can be stopped, e.g., by heating or the addition of sodiumbisulfite. Other methods of stopping fermentation include adding aperoxide (e.g., peroxy acetic acid or hydrogen peroxide), addingsuccinic acid or a salt thereof, cooling the contents of the vessel, orreducing the oxygen sparge rate. Combinations of any two or more ofthese methods may be used. If fermentation is to be conducted orcompleted during transport, the transportation vessel (e.g., the tank ofa rail car or tanker truck) can be fitted with a control unit thatincludes an oxygen monitor and ethanol monitor, and a delivery systemfor delivering sodium bisulfite (or other fermentation terminatingadditive) to the tank and/or a system for adjusting the parameters inthe tank to stop fermentation.

If desired, jet mixing can be utilized during fermentation, and iffermentation is conducted in the same vessel as saccharification thesame jet mixing equipment can be utilized. However, in some embodimentsjet mixing is not necessary. For example, if fermentation is conductedduring transport the movement of the rail car or tanker truck mayprovide adequate agitation.

Dispersing, Wet Milling, and Mixing

Systems are disclosed herein that include one or more tanks, one or moreagitators, e.g., one or more jet head agitators, and one or more wetmills. In some instances, all mills and agitator heads are within tanks.

Dispersing

The optional dispersing unit 134 may include any type of dispersingequipment that wets the feedstock with the liquid medium. Manydispersing units include a chamber and a rotor in the chamber positionedsuch that the feedstock and liquid medium are drawn towards the rotoraxially, and forced outward radially to the periphery of the rotor andthus through the outlet of the unit, in the manner of a centrifugalpump. Depending upon the construction of the dispersing unit, a back-uppump may be required (pump 139, discussed above) to draw the fluidthrough the dispersing unit at high viscosities. Some dispersing unitsare constructed to generate very high static fluid pressure within theunit; when such units are used a back-up pump is generally not required.

Example of suitable dispersing systems are disclosed in U.S. Ser. No.12/949,004, filed Nov. 18, 2010, the full disclosure of which isincorporated herein by reference.

Wet Milling

Two examples of wet milling heads for use in wet milling unit 160 areshown in FIGS. 4-10 and FIGS. 11-17. Each head includes a rotor and astator, and is mounted on a shaft (not shown) as is well known in therotor/stator mixer art. In both cases, when the rotor and stator areassembled, the gaps between the teeth of the rotor are out of alignmentwith the gaps between the teeth of the stator. This creates a shearinggap through which liquid flows under high shear during rotation of therotor.

Wet milling devices are commercially available, for example, from QuadroEngineering, (Waterloo Ontario), IKA Works Inc., (Wilmington, Del.),Admix Inc. (Manchester, N.H.) and Silverson, (Dartmouth Mass.).

In the implementation shown in FIGS. 4-10, the stator includes twoconcentric rings of teeth (see FIG. 6). Under a given set of conditions,this stator configuration will generally produce higher shear than thesingle ring stator configuration shown in FIGS. 11-17. On the otherhand, the rotor of the head shown in FIGS. 11-17 includes animpeller-like portion, as will be shown below, which provides a pumpingaction which may be desirable in certain cases.

Referring to FIGS. 4-10, head 162 includes a rotor 164 and a stator 166.The rotor and stator each include a central hub 158 and 159,respectively, which define apertures dimensioned to receive a shaft (notshown). The shaft is connected to a motor for rotation of the rotorwithin the stator, with the aperture in the rotor being keyed with theshaft and the shaft rotating freely within the aperture in the stator asis well known in the art.

Arms 161 and 163, respectively, extend from the hubs to support rotorand stator toothed rings. As shown in FIGS. 6 and 8, the stator 166includes two rings of teeth—an outer ring of teeth 170 and an inner ringof teeth 171. The rotor 164 includes a single ring of teeth 169, whichfit between the rings of the stator in a nested relationship. The uppersurface 165 of rotor 164 includes three projections 167 which createturbulence around the head.

As shown in FIG. 4A, a clearance a is provided between the outer surface168 of the teeth 169 of the rotor (the OD of the rotor) and the adjacentinner surface 172 of the outer ring of teeth 170 of the stator.Clearance a is preferably small, to generate high shear, and may be, forexample, from about 0.01 to 0.250 inch (0.25 to 0.64 mm), e.g., fromabout 0.03 to 0.10 inch (0.76 to 2.5 mm). The distance between the innerand outer rings of the stator is equal to this clearance plus the radialthickness of the teeth of the rotor, discussed below.

The outer diameters of the rotor and stator (OD1 and OD2, FIGS. 7 and 8)will depend on the volume of the tank in which the milling head is used,and how many milling heads are positioned in the tank. The outerdiameter of the stator, OD2, can be, for example, from about 3 to 50″,e.g., from about 5 to 25 inches, with larger heads being used in largertanks. As an example, a 4″ stator may be used in a 300 gallon tank.

As shown in FIG. 5, each tooth 170 on the outer ring of the statorincludes a chamfer 174 between its top surface 176 and outer side wall178.

The circumferential spacing between adjacent teeth is generally the samefor the rotor (S1, FIG. 9) and both rings of the stator (S2 and S3, FIG.10). Like the clearance a, this spacing will also affect the amount ofshear generated by the head during rotation of the stator, with a largerspacing resulting in reduced shear. In some implementations, the spacingS1, S2 and S3 is about 0.1 to 0.5 inch (2.5 to 12.5 mm).

The tooth size may vary to some extent based on the desired headdiameter, with larger heads having in some cases somewhat larger teethfor durability. However, generally the tooth size and tooth spacing willremain relatively constant as head diameter increases, with the numberof teeth increasing with increasing head diameter. Referring to FIGS. 9and 10, in some implementations the tooth dimensions can be, forexample, as follows:

T1: 0.10″

T2: 0.35″

T3: 0.10″

T4: 0.30″

T5: 0.10″

T6: 0.30″

where T1 is the radial thickness of the rotor teeth, T2 is thecircumferential thickness of the rotor teeth, T3 is the radial thicknessof the outer stator teeth, T4 is the circumferential thickness of theouter stator teeth, and T5 and T6 are, respectively, the radial andcircumferential thicknesses of the inner stator teeth.

As noted above, an alternative embodiment is shown in FIGS. 11-17, inwhich the stator has only a single row of teeth. This embodiment alsodiffers from that shown in FIGS. 4-10 in other respects.

First, the arms 1161 of the rotor are curved in two planes, as shown inFIGS. 11-13, causing the rotor to act as an impeller in addition to itsshearing action in the rotor/stator arrangement. This impellerfunctionality is enhanced by the presence of three larger teeth 1180(see FIGS. 13 and 14) in the rotor ring, which act as extensions of therotor arms.

Second, the adjacent side walls 1182 of the teeth 1169 of the rotor arenot arranged at an angle R with respect to the radii of the ring, asbest seen in FIGS. 14 and 16. This angle may be, for example, from about0 to 30 degrees. The angle of the teeth helps to pump material throughthe gap.

The dimensions of the rotor and stator in this embodiment are generallythe same as those described above for the embodiment shown in FIGS.11-17.

The rotor or stator can be made with a variety of materials. Forexample, ceramics (e.g., oxides, carbides or nitrides), stainless steel,or super alloys (e.g., Hastelloy, Inconel, Waspaloy, Ren alloys, Haynesalloys, TMS alloys and CMSX single crystal alloys). The rotor/statorhead is in some cases interchangeable with the jet mixing headsdescribed below, in particular those shown in FIGS. 19-19B. For example,in the case of converting a jet mixer to a rotor/stator, shroud 208(FIG. 19) and mixing element 206 (FIG. 19A) are removed and therotor/stator head is mounted on shaft 204.

FIG. 20 shows a cross-sectional view of a system for wet milling thatincludes a tank (252), two motors (250) two shafts (254), a wet millinghead (256) and a jet mixer head (258). As shown, one of the shafts isconnected to one of the motors on one end and a wet milling head, asdescribed above. Also as shown, the other shaft is connected to theother motor on one end and a jet milling head on the other end.

Jet Mixing

Particularly advantageous mixers for use during saccharification andfermentation are known as “jet mixers.” In general, suitable mixers havein common that they produce high velocity circulating flow, for exampleflow in a toroidal or elliptical pattern. Generally, preferred mixersexhibit a high bulk flow rate. Preferred mixers provide this mixingaction with relatively low energy consumption. It is also generallypreferred that the mixer produce relatively low shear and avoid heatingof the liquid medium, as shear and/or heat can deleteriously affect thesaccharifying agent (or microorganism, e.g., in the case offermentation). As will be discussed in detail below, some preferredmixers draw the mixture through an inlet into a mixing element, whichmay include a rotor or impeller, and then expel the mixture from themixing element through an outlet nozzle. This circulating action, andthe high velocity of the jet exiting the nozzle, assist in dispersingmaterial that is floating on the surface of the liquid or material thathas settled to the bottom of the tank, depending on the orientation ofthe mixing element. Mixing elements can be positioned in differentorientations to disperse both floating and settling material, and theorientation of the mixing elements can in some cases be adjustable.

In some preferred mixing systems the velocity v_(o) of the jet as meetsthe ambient fluid is from about 2 to 300 m/s, e.g., about 5 to 150 m/sor about 10 to 100 m/s. The power consumption of the mixing system maybe about 20 to 1000 KW, e.g., 30 to 570 KW, 50 to 500 KW, or 150 to 250KW for a 100,000 L tank.

Jet mixing involves the discharge of a submerged jet, or a number ofsubmerged jets, of high velocity liquid into a fluid medium, in thiscase the mixture of biomass feedstock, liquid medium and saccharifyingagent. The jet of liquid penetrates the fluid medium, with its energybeing dissipated by turbulence and some initial heat. This turbulence isassociated with velocity gradients (fluid shear). The surrounding fluidis accelerated and entrained into the jet flow, with this secondaryentrained flow increasing as the distance from the jet nozzle increases.The momentum of the secondary flow remains generally constant as the jetexpands, as long as the flow does not hit a wall, floor or otherobstacle. The longer the flow continues before it hits any obstacle, themore liquid is entrained into the secondary flow, increasing the bulkflow in the tank or vessel. When it encounters an obstacle, thesecondary flow will lose momentum, more or less depending on thegeometry of the tank, e.g., the angle at which the flow impinges on theobstacle. It is generally desirable to orient the jets and/or design thetank so that hydraulic losses to the tank walls are minimized. Forexample, it may be desirable for the tank to have an arcuate bottom(e.g., a domed headplate), and for the jet mixers to be orientedrelatively close to the sidewalls. The tank bottom (lower head plate)may have any desired domed configuration, or may have an elliptical orconical geometry.

Jet mixing differs from most types of liquid/liquid and liquid/solidmixing in that the driving force is hydraulic rather than mechanical.Instead of shearing fluid and propelling it around the mixing vessel, asa mechanical agitator does, a jet mixer forces fluid through one or morenozzles within the tank, creating high-velocity jets that entrain otherfluid. The result is shear (fluid against fluid) and circulation, whichmix the tank contents efficiently.

Referring to FIG. 18, the high velocity gradient between the core flowfrom a submerged jet and the surrounding fluid causes eddies. FIG. 18Aillustrates the general characteristics of a submerged jet. As thesubmerged jet expands into the surrounding ambient environment thevelocity profile flattens as the distance (x) from the nozzle increases.Also, the velocity gradient dv/dr changes with r (the distance from thecenterline of the jet) at a given distance x, such that eddies arecreated which define the mixing zone (the conical expansion from thenozzle).

In an experimental study of a submerged jet in air (the results of whichare applicable to any fluid, including water), Albertson et al.(“Diffusion of Submerged Jets,” Paper 2409, Amer. Soc. of CivilEngineers Transactions, Vol. 115:639-697, 1950, at p. 657) developeddimensionless relationships for v(x)_(r=0)/v_(o) (centerline velocity),v(r)_(x)/v(x)_(r=0) (velocity profile at a given x), Q_(x)/Q_(o) (flowentrainment), and E_(x)/E_(o) (energy change with x):

(1)  Centerline  velocity, v(x)_(r = 0)/v_(o):                        ${\frac{v\left( {r = 0} \right)}{v_{o}}\frac{x}{D_{o}}} = 6.2$(2)  velocity  profile  at  any  x, v(r)_(x)/v(x)_(r = 0):                 ${\log \left\lbrack {\frac{{v(r)}_{x}}{v_{o}}\frac{x}{D}} \right\rbrack} = {0.79 - {33\frac{r^{2}}{x^{2}}}}$(3)  Flow  and  energy  at  any  x:                        $\begin{matrix}{\frac{Q_{x}}{Q_{o}} = {0.32\frac{x}{D_{o}}}} & (10.21) \\{\frac{E_{x}}{E_{o}} = {4.1\frac{D_{o}}{x}}} & (10.22)\end{matrix}$

where:v(r=0)=centerline velocity of submerged jet (m/s),v_(o)=velocity of jet as it emerges from the nozzle (m/s),x=distance from nozzle (m),r=distance from centerline of jet (m),D_(o)=diameter of nozzle (m),Q_(x)=flow of fluid across any given plane at distance x from the nozzle(me/s),Q_(o)=flow of fluid emerging from the nozzle (m3/s),E=energy flux of fluid across any given plane at distance x from thenozzle (m³/s),E_(o)=energy flux of fluid emerging from the nozzle (m³/s).

-   (“Water Treatment Unit Processes: Physical and Chemical,” David W.    Hendricks, CRC Press 2006, p. 411.)

Jet mixing is particularly cost-effective in large-volume (over 1,000gal) and low-viscosity (under 1,000 cPs) applications. It is alsogenerally advantageous that in most cases the pump or motor of the jetmixer not be submerged, e.g., when a pump is used it is generallylocated outside the vessel.

One advantage of jet mixing is that the temperature of the ambient fluid(other than directly adjacent the exit of the nozzle, where there may besome localized heating) is increased only slightly if at all. Forexample, the temperature may be increased by less than 5° C., less than1° C., or not to any measurable extent.

Jet-Flow Agitators

One type of jet-flow agitator is shown in FIGS. 19-19A. This type ofmixer is available commercially, e.g., from IKA under the tradenameROTOTRON™. Referring to FIG. 19, the mixer 200 includes a motor 202,which rotates a drive shaft 204. A mixing element 206 is mounted at theend of the drive shaft 204. As shown in FIG. 19A, the mixing element 206includes a shroud 208 and, within the shroud, an impeller 210. Asindicated by the arrows, when the impeller is rotated in its “forward”direction, the impeller 210 draws liquid in through the open upper end212 of the shroud and forces the liquid out through the open lower end214. Liquid exiting end 214 is in the form of a high velocity stream orjet. If the direction of rotation of the impeller 210 is reversed,liquid can be drawn in through the lower end 214 and ejected through theupper end 212. This can be used, for example, to suck in solids that arefloating near or on the surface of the liquid in a tank or vessel. (Itis noted that “upper” and “lower” refer to the orientation of the mixerin FIG. 19; the mixer may be oriented in a tank so that the upper end isbelow the lower end.)

The shroud 208 includes flared areas 216 and 218 adjacent its ends.These flared areas are believed to contribute to the generally toroidalflow that is observed with this type of mixer. The geometry of theshroud and impeller also concentrate the flow into a high velocitystream using relatively low power consumption.

Preferably, the clearance between the shroud 208 and the impeller 210 issufficient so as to avoid excessive milling of the material as it passesthrough the shroud. For example, the clearance may be at least 10 timesthe average particle size of the solids in the mixture, preferably atleast 100 times.

In some implementations, the shaft 204 is configured to allow gasdelivery through the shaft. For example, the shaft 204 may include abore (not shown) through which gas is delivered, and one or moreorifices through which gas exits into the mixture. The orifices may bewithin the shroud 208, to enhance mixing, and/or at other locationsalong the length of the shaft 204.

The impeller 210 may have any desired geometry that will draw liquidthrough the shroud at a high velocity. The impeller is preferably amarine impeller, as shown in FIG. 19A, but may have a different design,for example, a Rushton impeller as shown in FIG. 19B, or a modifiedRushton impeller, e.g., tilted so as to provide some axial flow.

In order to generate the high velocity flow through the shroud, themotor 202 is preferably a high speed, high torque motor, e.g., capableof operating at 500 to 20,000 RPM, e.g., 3,000 to 10,000 RPM. However,the larger the mixer (e.g., the larger the shroud and/or the larger themotor) the lower the rotational speed can be. Thus, if a large mixer isused, such as a 5 hp, 10 hp, 20 hp, or 30 hp or greater, the motor maybe designed to operate at lower rotational speeds, e.g., less than 2000RPM, less than 1500 RPM, or even 500 RPM or less. For example, a mixersized to mix a 10,000-20,000 liter tank may operate at speeds of 900 to1,200 RPM. The torque of the motor is preferably self-adjusting, tomaintain a relatively constant impeller speed as the mixing conditionschange over time, e.g., due to saccharification of the solids.

Advantageously, the mixer can be oriented at any desired angle orlocation in the tank, to direct the jet flow in a desired direction.Moreover, as discussed above, depending on the direction of rotation ofthe impeller the mixer can be used to draw fluid from either end of theshroud.

In some implementations, two or more jet mixers are positioned in thevessel, with one or more being configured to jet fluid upward (“uppump”) and one or more being configured to jet fluid downward (“downpump”). In some cases, an up pumping mixer will be positioned adjacent adown pumping mixer, to enhance the turbulent flow created by the mixers.If desired, one or more mixers may be switched between upward flow anddownward flow during processing. It may be advantageous to switch all ormost of the mixers to up pumping mode during initial dispersion of thefeedstock in the liquid medium, particularly if the feedstock is dumpedor blown onto the surface of the liquid, as up pumping createssignificant turbulence at the surface. Up pumping can also be usedduring fermentation to help remove CO₂ from the liquid by causing thegas to bubble to the surface where it can be vented.

Other suitable jet mixers are described in U.S. application Ser. No.12/782,694 filed May 18, 2011; Ser. No. 13/293,985 filed Nov. 10, 2011;Ser. No. 13/293,977 filed Nov. 10, 2011 and U.S. Ser. No. 12/782,694,filed May 18, 2010, the full disclosures of which are incorporatedherein by reference.

Materials Biomass Materials

The biomass can be, e.g., a cellulosic or lignocellulosic material. Suchmaterials include paper and paper products (e.g., polycoated paper andKraft paper), wood, wood-related materials, e.g., particle board,grasses, rice hulls, bagasse, jute, hemp, flax, bamboo, sisal, abaca,straw, switchgrass, alfalfa, hay, corn cobs, corn stover, wheat straw,coconut hair; and materials high in α-cellulose content, e.g., cotton.Feedstocks can be obtained from virgin scrap textile materials, e.g.,remnants, post consumer waste, e.g., rags. When paper products are usedthey can be virgin materials, e.g., scrap virgin materials, or they canbe post-consumer waste. Aside from virgin raw materials, post-consumer,industrial (e.g., offal), and processing waste (e.g., effluent frompaper processing) can also be used as fiber sources. Biomass feedstockscan also be obtained or derived from human (e.g., sewage), animal orplant wastes. Additional cellulosic and lignocellulosic materials havebeen described in U.S. Pat. Nos. 6,448,307; 6,258,876; 6,207,729;5,973,035 and 5,952,105.

In some embodiments, the biomass material includes a carbohydrate thatis or includes a material having one or more β-1,4-linkages and having anumber average molecular weight between about 3,000 and 50,000. Such acarbohydrate is or includes cellulose (I), which is derived from(β-glucose 1) through condensation of β(1,4)-glycosidic bonds. Thislinkage contrasts itself with that for α(1,4)-glycosidic bonds presentin starch and other carbohydrates.

In some embodiments, the biomass material includes starchy materials,e.g., corn starch, wheat starch, potato starch or rice starch, aderivative of starch, or a material that includes starch, such as anedible food product or a crop. For example, the starchy material can bearracacha, buckwheat, banana, barley, corn kernels, cassava, kudzu, oca,sago, sorghum, regular household potatoes, sweet potato, taro, yams, orone or more beans, such as favas, lentils or peas. Blends of any two ormore starchy materials are also starchy materials. Mixtures of starchy,cellulosic and or lignocellulosic materials can also be used. Forexample, a biomass can be an entire plan, a part of a plant or differentparts of a plant e.g., a wheat plant, cotton plant, a corn plant, riceplant or a tree. The starchy materials can be treated by any of themethods described herein.

In other embodiments, the biomass materials, such as cellulosic, starchyand lignocellulosic feedstock materials, can be obtained from plantsthat have been modified with respect to a wild type variety. Suchmodifications may be, for example, through the iterative steps ofselection and breeding to obtain desired traits in a plant. Furthermore,the plants can have had genetic material removed, modified, silencedand/or added with respect to the wild type variety. For example,genetically modified plants can be produced by recombinant DNA methods,where genetic modifications include introducing or modifying specificgenes from parental varieties, or, for example, by using transgenicbreeding wherein a specific gene or genes are introduced to a plant froma different species of plant and/or bacteria. Another way to creategenetic variation is through mutation breeding wherein new alleles areartificially created from endogeneous genes. The artificial genes can becreated by a variety of ways including treating the plant or seeds with,for example, chemical mutagens (e.g., using alkylating agents, epoxides,alkaloids, peroxides, formaldehyde), irradiation (e.g., X-rays, gammarays, neutrons, beta particles, alpha particles, protons, deuterons, UVradiation) and temperature shocking or other external stressing andsubsequent selection techniques. Other methods of providing modifiedgenes is through error prone PCR and DNA shuffling followed by insertionof the desired modified DNA into the desired plant or seed. Methods ofintroducing the desired genetic variation in the seed or plant include,for example, the use of a bacterial carrier, biolistics, calciumphosphate precipitation, electroporation, gene splicing, gene silencing,lipofection, microinjection and viral carriers. Additional geneticallymodified materials have been described in U.S. application Ser. No.13/396,369 filed Feb. 14, 2012 the full disclosure of which isincorporated herein by reference.

In some cases the biomass is a microbial material. Microbial sourcesinclude, but are not limited to, any naturally occurring or geneticallymodified microorganism or organism that contains or is capable ofproviding a source of carbohydrates (e.g., cellulose), for example,protists, e.g., animal protists (e.g., protozoa such as flagellates,amoeboids, ciliates, and sporozoa) and plant protists (e.g., algae suchalveolates, chlorarachniophytes, cryptomonads, euglenids, glaucophytes,haptophytes, red algae, stramenopiles, and viridaeplantae). Otherexamples include seaweed, plankton (e.g., macroplankton, mesoplankton,microplankton, nanoplankton, picoplankton, and femptoplankton),phytoplankton, bacteria (e.g., gram positive bacteria, gram negativebacteria, and extremophiles), yeast and/or mixtures of these. In someinstances, microbial biomass can be obtained from natural sources, e.g.,the ocean, lakes, bodies of water, e.g., salt water or fresh water, oron land. Alternatively or in addition, microbial biomass can be obtainedfrom culture systems, e.g., large scale dry and wet culture systems.

Saccharifying Agents

Suitable enzymes include cellobiases, cellulases and amylases capable ofdegrading biomass.

Suitable cellobiases include a cellobiase from Aspergillus niger soldunder the tradename NOVOZYME 188™.

Cellulases are capable of degrading biomass, and may be of fungal orbacterial origin. Suitable enzymes include cellulases from the generaBacillus, Pseudomonas, Humicola, Fusarium, Thielavia, Acremonium,Chrysosporium and Trichoderma, and include species of Humicola,Coprinus, Thielavia, Fusarium, Myceliophthora, Acremonium,Cephalosporium, Scytalidium, Penicillium or Aspergillus (see, e.g., EP458162), especially those produced by a strain selected from the speciesHumicola insolens (reclassified as Scytalidium thermophilum, see, e.g.,U.S. Pat. No. 4,435,307), Coprinus cinereus, Fusarium oxysporum,Myceliophthora thermophila, Meripilus giganteus, Thielavia terrestris,Acremonium sp., Acremonium persicinum, Acremonium acremonium, Acremoniumbrachypenium, Acremonium dichromosporum, Acremonium obclavatum,Acremonium pinkertoniae, Acremonium roseogriseum, Acremoniumincoloratum, and Acremonium furatum; preferably from the speciesHumicola insolens DSM 1800, Fusarium oxysporum DSM 2672, Myceliophthorathermophila CBS 117.65, Cephalosporium sp. RYM-202, Acremonium sp. CBS478.94, Acremonium sp. CBS 265.95, Acremonium persicinum CBS 169.65,Acremonium acremonium AHU 9519, Cephalosporium sp. CBS 535.71,Acremonium brachypenium CBS 866.73, Acremonium dichromosporum CBS683.73, Acremonium obclavatum CBS 311.74, Acremonium pinkertoniae CBS157.70, Acremonium roseogriseum CBS 134.56, Acremonium incoloratum CBS146.62, and Acremonium furatum CBS 299.70H. Cellulolytic enzymes mayalso be obtained from Chrysosporium, preferably a strain ofChrysosporium lucknowense. Additionally, Trichoderma (particularlyTrichoderma viride, Trichoderma reesei, and Trichoderma koningii),alkalophilic Bacillus (see, for example, U.S. Pat. No. 3,844,890 and EP458162), and Streptomyces (see, e.g., EP 458162) may be used. Enzymecomplexes may be utilized, such as those available from Genencore underthe tradename ACCELLERASE®, for example, Accellerase® 1500 enzymecomplex. Accellerase® 1500 enzyme complex contains multiple enzymeactivities, mainly exoglucanase, endoglucanase (2200-2800 CMC U/g),hemi-cellulase, and beta-glucosidase (525-775 pNPG U/g), and has a pH of4.6 to 5.0. The endoglucanase activity of the enzyme complex isexpressed in carboxymethylcellulose activity units (CMC U), while thebeta-glucosidase activity is reported in pNP-glucoside activity units(pNPG U). In one embodiment, a blend of Accellerase® 1500 enzyme complexand NOVOZYME™ 188 cellobiase is used.

In some implementations, the saccharifying agent comprises an acid,e.g., a mineral acid. When an acid is used, co-products may be generatedthat are toxic to microorganisms, in which case the process can furtherinclude removing such co-products. Removal may be performed using anactivated carbon, e.g., activated charcoal, or other suitabletechniques.

Fermentation Agents

The microorganism(s) used in fermentation can be natural microorganismsand/or engineered microorganisms. For example, the microorganism can bea bacterium, e.g., a cellulolytic bacterium, a fungus, e.g., a yeast, aplant or a protist, e.g., an algae, a protozoa or a fungus-like protist,e.g., a slime mold. When the organisms are compatible, mixtures oforganisms can be utilized.

Suitable fermenting microorganisms have the ability to convertcarbohydrates, such as glucose, xylose, arabinose, mannose, galactose,oligosaccharides or polysaccharides into fermentation products.Fermenting microorganisms include strains of the genus Saccharomycesspp. e.g., Saccharomyces cerevisiae (baker's yeast), Saccharomycesdistaticus, Saccharomyces uvarum; the genus Kluyveromyces, e.g., speciesKluyveromyces marxianus, Kluyveromyces fragilis; the genus Candida,e.g., Candida pseudotropicalis, and Candida brassicae, Pichia stipitis(a relative of Candida shehatae, the genus Clavispora, e.g., speciesClavispora lusitaniae and Clavispora opuntiae, the genus Pachysolen,e.g., species Pachysolen tannophilus, the genus Bretannomyces, e.g.,species Bretannomyces clausenii (Philippidis, G. P., 1996, Cellulosebioconversion technology, in Handbook on Bioethanol: Production andUtilization, Wyman, C. E., ed., Taylor & Francis, Washington, D.C.,179-212). Other suitable microorganisms include, for example, Zymomonasmobilis, Clostridium thermocellum (Philippidis, 1996, supra),Clostridium saccharobutylacetonicum, Clostridium saccharobutylicum,Clostridium Puniceum, Clostridium beijernckii, Clostridiumacetobutylicum, Moniliella pollinis, Yarrowia lipolytica, Aureobasidiumsp., Trichosporonoides sp., Trigonopsis variabilis, Trichosporon sp.,Moniliellaacetoabutans, Typhula variabilis, Candida magnoliae,Ustilaginomycetes, Pseudozyma tsukubaensis, yeast species of generaZygosaccharomyces, Debaryomyces, Hansenula and Pichia, and fungi of thedematioid genus Torula.

Commercially available yeasts include, for example, Red Star®/LesaffreEthanol Red (available from Red Star/Lesaffre, USA), FALI® (availablefrom Fleischmann's Yeast, a division of Burns Philip Food Inc., USA),SUPERSTART® (available from Alltech, now Lalemand), GERT STRAND®(available from Gert Strand AB, Sweden) and FERMOL® (available from DSMSpecialties).

Additives Antibiotics

While it is generally preferred to have a high sugar concentration inthe saccharified solution, lower concentrations may be used, in whichcase it may be desirable to add an antimicrobial additive, e.g., a broadspectrum antibiotic, in a low concentration, e.g., 50 to 150 ppm. Othersuitable antibiotics include amphotericin B, ampicillin,chloramphenicol, ciprofloxacin, gentamicin, hygromycin B, kanamycin,neomycin, penicillin, puromycin, streptomycin. Antibiotics will inhibitgrowth of microorganisms during transport and storage, and can be usedat appropriate concentrations, e.g., between 15 and 1000 ppm by weight,e.g., between 25 and 500 ppm, or between 50 and 150 ppm. If desired, anantibiotic can be included even if the sugar concentration is relativelyhigh.

Surfactants

The addition of surfactants can enhance the rate of saccharification.Examples of surfactants include non-ionic surfactants, such as a Tween®20 or Tween® 80 polyethylene glycol surfactants, ionic surfactants, oramphoteric surfactants. Other suitable surfactants include octylphenolethoxylates such as the TRITON™ X series nonionic surfactantscommercially available from Dow Chemical. A surfactant can also be addedto keep the sugar that is being produced in solution, particularly inhigh concentration solutions.

Saccharification Medium

In one embodiment, the medium has the following concentrations ofcomponents:

Yeast nitrogen base 1.7 g/L Urea 2.27 g/L Peptone 6.56 g/L Tween ® 80surfactant 10 g/L

Physical Treatment of Feedstock Physical Preparation

In some cases, methods can include a physical preparation, e.g., sizereduction of materials, such as by cutting, grinding, shearing,pulverizing or chopping. For example, in other cases, material is firstpretreated or processed using one or more of the methods describedherein, such as radiation, sonication, oxidation, pyrolysis or steamexplosion, and then size reduced or further size reduced. Treating firstand then size reducing can be advantageous. Screens and/or magnets canbe used to remove oversized or undesirable objects such as, for example,rocks or nails from the feed stream. In some cases no pre-processing isnecessary, for example when the initial recalcitrance of the biomass islow, and wet milling is sufficiently effective to reduce therecalcitrance, for example, to prepared the material for furtherprocessing, e.g., saccharification.

Feed preparation systems can be configured to produce streams withspecific characteristics such as, for example, specific maximum sizes,specific length-to-width, or specific surface areas ratios. Physicalpreparation can increase the rate of reactions or reduce the processingtime required by opening up the materials and making them moreaccessible to processes and/or reagents, such as reagents in a solution.The bulk density of feedstocks can be controlled (e.g., increased). Insome situations, it can be desirable to prepare a high or higher bulkdensity material, e.g., by densifying the material (e.g., densificationcan make it easier and less costly to transport to another site) andthen reverting the material to a lower bulk density state. The materialcan be densified, for example from less than 0.2 g/cc to more than 0.9g/cc (e.g., less than 0.3 to more than 0.5 g/cc, less than 0.3 to morethan 0.9 g/cc, less than 0.5 to more than 0.9 g/cc, less than 0.3 tomore than 0.8 g/cc, less than 0.2 to more than 0.5 g/cc). For example,the material can be densified by the methods and equipment disclosed inU.S. Pat. No. 7,932,065 and WO 2008/073186, the full disclosures ofwhich are incorporated herein by reference. Densified materials can beprocessed by any of the methods described herein, or any materialprocessed by any of the methods described herein can be subsequentlydensified. In some cases, the material can be densified prior to wetmilling. Wet milling can re-open densified material.

Size Reduction

In some embodiments, the material to be processed is in the form of afibrous material that includes fibers provided by shearing a fibersource. For example, the shearing can be performed with a rotary knifecutter.

For example, a fiber source, e.g., that is recalcitrant or that has hadits recalcitrance level reduced, can be sheared, e.g., in a rotary knifecutter, to provide a first fibrous material. The first fibrous materialis passed through a first screen, e.g., having an average opening sizeof 1.59 mm or less ( 1/16 inch, 0.0625 inch), provide a second fibrousmaterial. If desired, the fiber source can be cut prior to the shearing,e.g., with a shredder. For example, when a paper is used as the fibersource, the paper can be first cut into strips that are, e.g., ¼- to½-inch wide, using a shredder, e.g., a counter-rotating screw shredder,such as those manufactured by Munson (Utica, N.Y.). As an alternative toshredding, the paper can be reduced in size by cutting to a desired sizeusing a guillotine cutter. For example, the guillotine cutter can beused to cut the paper into sheets that are, e.g., 10 inches wide by 12inches long.

In some embodiments, the shearing of the fiber source and the passing ofthe resulting first fibrous material through a first screen areperformed concurrently. The shearing and the passing can also beperformed in a batch-type process.

For example, a rotary knife cutter can be used to concurrently shear thefiber source and screen the first fibrous material. A rotary knifecutter includes a hopper that can be loaded with a shredded fiber sourceprepared by shredding a fiber source. The shredded fiber source In someimplementations, the feedstock is physically treated prior tosaccharification and/or fermentation. Physical treatment processes caninclude one or more of any of those described herein, such as mechanicaltreatment, chemical treatment, irradiation, sonication, oxidation,pyrolysis or steam explosion. Treatment methods can be used incombinations of two, three, four, or even all of these technologies (inany order). When more than one treatment method is used, the methods canbe applied at the same time or at different times. Other processes thatchange a molecular structure of a biomass feedstock may also be used,alone or in combination with the processes disclosed herein.

Mechanical Treatments

In some cases, methods can include mechanically treating the biomassfeedstock. Mechanical treatments include, for example, cutting, milling,pressing, grinding, shearing and chopping. Milling may include, forexample, ball milling, hammer milling, rotor/stator dry or wet milling,freezer milling, blade milling, knife milling, disk milling, rollermilling or other types of milling. Other mechanical treatments include,e.g., stone grinding, cracking, mechanical ripping or tearing, pingrinding or air attrition milling.

Mechanical treatment can be advantageous for “opening up,” “stressing,”breaking and shattering the cellulosic or lignocellulosic materials,making the cellulose of the materials more susceptible to chain scissionand/or reduction of crystallinity. The open materials can also be moresusceptible to oxidation when irradiated.

In some cases, the mechanical treatment may include an initialpreparation of the feedstock as received, e.g., size reduction ofmaterials, such as by cutting, grinding, shearing, pulverizing orchopping. For example, in some cases, loose feedstock (e.g., recycledpaper, starchy materials, or switchgrass) is prepared by shearing orshredding.

Alternatively, or in addition, the feedstock material can first bephysically treated by one or more of the other physical treatmentmethods, e.g., chemical treatment, radiation, sonication, oxidation,pyrolysis or steam explosion, and then mechanically treated. Thissequence can be advantageous since materials treated by one or more ofthe other treatments, e.g., irradiation or pyrolysis, tend to be morebrittle and, therefore, it may be easier to further change the molecularstructure of the material by mechanical treatment.

In some embodiments, the feedstock material is in the form of a fibrousmaterial, and mechanical treatment includes shearing to expose fibers ofthe fibrous material. Shearing can be performed, for example, using arotary knife cutter. Other methods of mechanically treating thefeedstock include, for example, milling or grinding. Milling may beperformed using, for example, a hammer mill, ball mill, colloid mill,conical or cone mill, disk mill, edge mill, Wiley mill or grist mill.Grinding may be performed using, for example, a stone grinder, pingrinder, coffee grinder, or burr grinder. Grinding may be provided, forexample, by a reciprocating pin or other element, as is the case in apin mill. Other mechanical treatment methods include mechanical rippingor tearing, other methods that apply pressure to the material, and airattrition milling. Suitable mechanical treatments further include anyother technique that changes the molecular structure of the feedstock.

If desired, the mechanically treated material can be passed through ascreen, e.g., having an average opening size of 1.59 mm or less ( 1/16inch, 0.0625 inch). In some embodiments, shearing, or other mechanicaltreatment, and screening are performed concurrently. For example, arotary knife cutter can be used to concurrently shear and screen thefeedstock. The feedstock is sheared between stationary blades androtating blades to provide a sheared material that passes through ascreen, and is captured in a bin.

The cellulosic or lignocellulosic material can be mechanically treatedin a dry state (e.g., having little or no free water on its surface), ahydrated state (e.g., having up to ten percent by weight absorbedwater), or in a wet state, e.g., having between about 10 percent andabout 75 percent by weight water. The fiber source can even bemechanically treated while partially or fully submerged under a liquid,such as water, ethanol or isopropanol.

The fiber cellulosic or lignocellulosic material can also bemechanically treated under a gas (such as a stream or atmosphere of gasother than air), e.g., oxygen or nitrogen, or steam.

If desired, lignin can be removed from any of the fibrous materials thatinclude lignin. Also, to aid in the breakdown of the materials thatinclude cellulose, the material can be treated prior to or duringmechanical treatment or irradiation with heat, a chemical (e.g., mineralacid, base or a strong oxidizer such as sodium hypochlorite) and/or anenzyme. For example, grinding can be performed in the presence of anacid.

Mechanical treatment systems can be configured to produce streams withspecific morphology characteristics such as, for example, surface area,porosity, bulk density, and, in the case of fibrous feedstocks, fibercharacteristics such as length-to-width ratio.

In some embodiments, a BET surface area of the mechanically treatedmaterial is greater than 0.1 m²/g, e.g., greater than 0.25 m²/g, greaterthan 0.5 m²/g, greater than 1.0 m²/g, greater than 1.5 m²/g, greaterthan 1.75 m²/g, greater than 5.0 m²/g, greater than 10 m²/g, greaterthan 25 m²/g, greater than 35 m²/g, greater than 50 m²/g, greater than60 m²/g, greater than 75 m²/g, greater than 100 m²/g, greater than 150m²/g, greater than 200 m²/g, or even greater than 250 m²/g.

A porosity of the mechanically treated material can be, e.g., greaterthan 20 percent, greater than 25 percent, greater than 35 percent,greater than 50 percent, greater than 60 percent, greater than 70percent, greater than 80 percent, greater than 85 percent, greater than90 percent, greater than 92 percent, greater than 94 percent, greaterthan 95 percent, greater than 97.5 percent, greater than 99 percent, oreven greater than 99.5 percent.

In some embodiments, after mechanical treatment the material has a bulkdensity of less than 0.25 g/cm³, e.g., 0.20 g/cm³, 0.15 g/cm³, 0.10g/cm³, 0.05 g/cm³ or less, e.g., 0.025 g/cm³. Bulk density is determinedusing ASTM D1895B. Briefly, the method involves filling a measuringcylinder of known volume with a sample and obtaining a weight of thesample. The bulk density is calculated by dividing the weight of thesample in grams by the known volume of the cylinder in cubiccentimeters.

If the feedstock is a fibrous material the fibers of the fibrousmaterials mechanically treated material can have a relatively largeaverage length-to-diameter ratio (e.g., greater than 20-to-1), even ifthey have been sheared more than once. In addition, the fibers of thefibrous materials described herein may have a relatively narrow lengthand/or length-to-diameter ratio distribution.

As used herein, average fiber widths (e.g., diameters) are thosedetermined optically by randomly selecting approximately 5,000 fibers.Average fiber lengths are corrected length-weighted lengths. BET(Brunauer, Emmet and Teller) surface areas are multi-point surfaceareas, and porosities are those determined by mercury porosimetry.

If the second feedstock is a fibrous material 14 the averagelength-to-diameter ratio of fibers of the mechanically treated materialcan be, e.g. greater than 8/1, e.g., greater than 10/1, greater than15/1, greater than 20/1, greater than 25/1, or greater than 50/1. Anaverage fiber length of the mechanically treated material 14 can be,e.g., between about 0.5 mm and 2.5 mm, e.g., between about 0.75 mm and1.0 mm, and an average width (e.g., diameter) of the second fibrousmaterial 14 can be, e.g., between about 5 μm and 50 μm, e.g., betweenabout 10 μm and 30 μm.

In some embodiments, if the feedstock is a fibrous material, thestandard deviation of the fiber length of the mechanically treatedmaterial can be less than 60 percent of an average fiber length of themechanically treated material, e.g., less than 50 percent of the averagelength, less than 40 percent of the average length, less than 25 percentof the average length, less than 10 percent of the average length, lessthan 5 percent of the average length, or even less than 1 percent of theaverage length.

Treatment to Solubilize, Reduce Recalcitrance or Functionalize

Materials that have or have not been physically prepared can be treatedfor use in any production process described herein. One or more of theproduction processes described below may be included in therecalcitrance reducing operating unit discussed above. Alternatively, orin addition, other processes for reducing recalcitrance may be included.

Treatment processes utilized by the recalcitrance reducing operatingunit can include one or more of irradiation, sonication, oxidation,pyrolysis or steam explosion. Treatment methods can be used incombinations of two, three, four, or even all of these technologies (inany order).

Radiation Treatment

One or more radiation processing sequences can be used to processmaterials from the feedstock, and to provide a wide variety of differentsources to extract useful substances from the feedstock, and to providepartially degraded structurally modified material which functions asinput to further processing steps and/or sequences. Irradiation can, forexample, reduce the molecular weight and/or crystallinity of feedstock.Radiation can also sterilize the materials, or any media needed tobioprocess the material.

In some embodiments, energy deposited in a material that releases anelectron from its atomic orbital is used to irradiate the materials. Theradiation may be provided by (1) heavy charged particles, such as alphaparticles or protons, (2) electrons, produced, for example, in betadecay or electron beam accelerators, or (3) electromagnetic radiation,for example, gamma rays, x rays, or ultraviolet rays. In one approach,radiation produced by radioactive substances can be used to irradiatethe feedstock. In some embodiments, any combination in any order orconcurrently of (1) through (3) may be utilized. In another approach,electromagnetic radiation (e.g., produced using electron beam emitters)can be used to irradiate the feedstock. The doses applied depend on thedesired effect and the particular feedstock.

In some instances when chain scission is desirable and/or polymer chainfunctionalization is desirable, particles heavier than electrons, suchas protons, helium nuclei, argon ions, silicon ions, neon ions, carbonions, phosphorus ions, oxygen ions or nitrogen ions can be utilized.When ring-opening chain scission is desired, positively chargedparticles can be utilized for their Lewis acid properties for enhancedring-opening chain scission. For example, when maximum oxidation isdesired, oxygen ions can be utilized, and when maximum nitration isdesired, nitrogen ions can be utilized. The use of heavy particles andpositively charged particles is described in U.S. Pat. No. 7,931,784,the full disclosure of which is incorporated herein by reference.

In one method, a first material that is or includes cellulose having afirst number average molecular weight (M_(N1)) is irradiated, e.g., bytreatment with ionizing radiation (e.g., in the form of gamma radiation,X-ray radiation, 100 nm to 280 nm ultraviolet (UV) light, a beam ofelectrons or other charged particles) to provide a second material thatincludes cellulose having a second number average molecular weight(M_(N2)) lower than the first number average molecular weight. Thesecond material (or the first and second material) can be combined witha microorganism (with or without enzyme treatment) that can utilize thesecond and/or first material or its constituent sugars or lignin toproduce an intermediate or a product, such as those described herein.

Since the second material includes cellulose having a reduced molecularweight relative to the first material, and in some instances, a reducedcrystallinity as well, the second material is generally moredispersible, swellable and/or soluble, e.g., in a solution containing amicroorganism and/or an enzyme. These properties make the secondmaterial easier to process and more susceptible to chemical, enzymaticand/or biological attack relative to the first material, which cangreatly improve the production rate and/or production level of a desiredproduct, e.g., ethanol. Radiation can also sterilize the materials orany media needed to bioprocess the material.

In some embodiments, the second material can have a level of oxidation(O₂) that is higher than the level of oxidation (O₁) of the firstmaterial. A higher level of oxidation of the material can aid in itsdispersability, swellability and/or solubility, further enhancing thematerial's susceptibility to chemical, enzymatic or biological attack.In some embodiments, to increase the level of the oxidation of thesecond material relative to the first material, the irradiation isperformed under an oxidizing environment, e.g., under a blanket of airor oxygen, producing a second material that is more oxidized than thefirst material. For example, the second material can have more hydroxylgroups, aldehyde groups, ketone groups, ester groups or carboxylic acidgroups, which can increase its hydrophilicity.

Ionizing Radiation

Each form of radiation ionizes the carbon-containing material viaparticular interactions, as determined by the energy of the radiation.Heavy charged particles primarily ionize matter via Coulomb scattering;furthermore, these interactions produce energetic electrons that mayfurther ionize matter. Alpha particles are identical to the nucleus of ahelium atom and are produced by the alpha decay of various radioactivenuclei, such as isotopes of bismuth, polonium, astatine, radon,francium, radium, several actinides, such as actinium, thorium, uranium,neptunium, curium, californium, americium, and plutonium.

When particles are utilized, they can be neutral (uncharged), positivelycharged or negatively charged. When charged, the charged particles canbear a single positive or negative charge, or multiple charges, e.g.,one, two, three or even four or more charges. In instances in whichchain scission is desired, positively charged particles may bedesirable, in part due to their acidic nature. When particles areutilized, the particles can have the mass of a resting electron, orgreater, e.g., 500, 1000, 1500, 2000, 10,000 or even 100,000 times themass of a resting electron. For example, the particles can have a massof from about 1 atomic unit to about 150 atomic units, e.g., from about1 atomic unit to about 50 atomic units, or from about 1 to about 25,e.g., 1, 2, 3, 4, 5, 10, 12 or 15 amu. Accelerators used to acceleratethe particles can be electrostatic DC, electrodynamic DC, RF linear,magnetic induction linear or continuous wave. For example, cyclotrontype accelerators are available from IBA, Belgium, such as theRhodotron® system, while DC type accelerators are available from RDI,now IBA Industrial, such as the Dynamitron®. Ions and ion acceleratorsare discussed in Introductory Nuclear Physics, Kenneth S. Krane, JohnWiley & Sons, Inc. (1988), Krsto Prelec, FIZIKA B 6 (1997) 4, 177-206,Chu, William T., “Overview of Light-Ion Beam Therapy” Columbus-Ohio,ICRU-IAEA Meeting, 18-20 Mar. 2006, Iwata, Y. et al.,“Alternating-Phase-Focused IH-DTL for Heavy-Ion Medical Accelerators”Proceedings of EPAC 2006, Edinburgh, Scotland and Leaner, C. M. et al.,“Status of the Superconducting ECR Ion Source Venus” Proceedings of EPAC2000, Vienna, Austria.

In some embodiments, a beam of electrons is used as the radiationsource. A beam of electrons has the advantages of high dose rates (e.g.,1, 5, or even 10 Mrad per second), high throughput, less containment,and less confinement equipment. Electrons can also be more efficient atcausing chain scission. In addition, electrons having energies of 4-10MeV can have a penetration depth of 5 to 30 mm or more, such as 40 mm.In some cases, multiple electron beam devices (e.g., multiple heads,often referred to as “horns”) are used to deliver multiple doses ofelectron beam radiation to the material. This high total beam power isusually achieved by utilizing multiple accelerating heads. For example,the electron beam device may include two, four, or more acceleratingheads. As one example, the electron beam device may include fouraccelerating heads, each of which has a beam power of 300 kW, for atotal beam power of 1200 kW. The use of multiple heads, each of whichhas a relatively low beam power, prevents excessive temperature rise inthe material, thereby preventing burning of the material, and alsoincreases the uniformity of the dose through the thickness of the layerof material. Irradiating with multiple heads is disclosed in U.S.application Ser. No. 13/276,192 filed Oct. 18, 2011, the completedisclosure of which is incorporated herein by reference.

Electron beams can be generated, e.g., by electrostatic generators,cascade generators, transformer generators, low energy accelerators witha scanning system, low energy accelerators with a linear cathode, linearaccelerators, and pulsed accelerators. Electrons as an ionizingradiation source can be useful, e.g., for relatively thin piles ofmaterials, e.g., less than 0.5 inch, e.g., less than 0.4 inch, 0.3 inch,0.2 inch, or less than 0.1 inch. In some embodiments, the energy of eachelectron of the electron beam is from about 0.3 MeV to about 2.0 MeV(million electron volts), e.g., from about 0.5 MeV to about 1.5 MeV, orfrom about 0.7 MeV to about 1.25 MeV.

Electron beam irradiation devices may be procured commercially from IonBeam Applications, Louvain-la-Neuve, Belgium or the Titan Corporation,San Diego, Calif. Typical electron energies can be 1 MeV, 2 MeV, 4.5MeV, 7.5 MeV, or 10 MeV. Typical electron beam irradiation device powercan be 1 kW, 5 kW, 10 kW, 20 kW, 50 kW, 100 kW, 250 kW, or 500 kW. Thelevel of depolymerization of the feedstock depends on the electronenergy used and the dose applied, while exposure time depends on thepower and dose. Typical doses may take values of 1 kGy, 5 kGy, 10 kGy,20 kGy, 50 kGy, 100 kGy, or 200 kGy. In a some embodiments energiesbetween 0.25-10 MeV (e.g., 0.5-0.8 MeV, 0.5-5 MeV, 0.8-4 MeV, 0.8-3 MeV,0.8-2 MeV or 0.8-1.5 MeV) can be used.

Electromagnetic Radiation

In embodiments in which the irradiating is performed withelectromagnetic radiation, the electromagnetic radiation can have, e.g.,energy per photon (in electron volts) of greater than 10² eV, e.g.,greater than 10³, 10⁴, 10⁵, 10⁶, or even greater than 10⁷ eV. In someembodiments, the electromagnetic radiation has energy per photon ofbetween 10⁴ and 10⁷, e.g., between 10⁵ and 10⁶ eV. The electromagneticradiation can have a frequency of, e.g., greater than 10¹⁶ Hz, greaterthan 10¹⁷ Hz, 10¹⁸, 10¹⁹, 10²⁰, or even greater than 10²¹ Hz. In someembodiments, the electromagnetic radiation has a frequency of between10¹⁸ and 10²² Hz, e.g., between 10¹⁹ to 10²¹ Hz.

Doses

In some embodiments, the irradiating (with any radiation source or acombination of sources) is performed until the material receives a doseof at least 0.25 Mrad, e.g., at least 1.0, 2.5, 5.0, 8.0, 10, 15, 20,25, 30, 35, 40, 50, or even at least 100 Mrad. In some embodiments, theirradiating is performed until the material receives a dose of between1.0 Mrad and 6.0 Mrad, e.g., between 1.5 Mrad and 4.0 Mrad, 2 Mrad and10 Mrad, 5 Mrad and 20 Mrad, 10 Mrad and 30 Mrad, 10 Mrad and 40 Mrad,or 20 Mrad and 50 Mrad.

In some embodiments, the irradiating is performed at a dose rate ofbetween 5.0 and 1500.0 kilorads/hour, e.g., between 10.0 and 750.0kilorads/hour or between 50.0 and 350.0 kilorads/hours.

In some embodiments, two or more radiation sources are used, such as twoor more ionizing radiations. For example, samples can be treated, in anyorder, with a beam of electrons, followed by gamma radiation and UVlight having wavelengths from about 100 nm to about 280 nm. In someembodiments, samples are treated with three ionizing radiation sources,such as a beam of electrons, gamma radiation, and energetic UV light.

Sonication, Pyrolysis and Oxidation

In addition to radiation treatment, the feedstock may be treated withany one or more of sonication, pyrolysis and oxidation. These treatmentprocesses are described in U.S. Ser. No. 12/417,840 filed Apr. 3, 2009,the disclosure of which is incorporated by reference herein.

Other Processes to Solubilize, Reduce Recalcitrance or to Functionalize

Any of the processes of this paragraph can be used alone without any ofthe processes described herein, or in combination with any of theprocesses described herein (in any order): steam explosion, chemicaltreatment (e.g., acid treatment (including concentrated and dilute acidtreatment with mineral acids, such as sulfuric acid, hydrochloric acidand organic acids, such as trifluoroacetic acid), and/or base treatment(e.g., treatment with lime or sodium hydroxide)), UV treatment, screwextrusion treatment, solvent treatment (e.g., treatment with ionicliquids) and freeze milling. Some of these processes, for example, aredescribed in U.S. Ser. No. 12/417,723 filed Apr. 3, 2009; Ser. No.13/099,151 filed May 2, 2011; and Ser. No. 12/502,629 filed Jul. 14,2009, the disclosures of which are incorporated herein.

Production of Fuels, Acids, Esters, and/or Other Products

After one or more of the processing steps discussed above have beenperformed on the biomass, the complex carbohydrates contained in thecellulose and hemicellulose fractions can be processed into fermentablesugars using a saccharification process, as discussed above.

After the resulting sugar solution has been transported to amanufacturing facility, the sugars can be converted into a variety ofproducts, such as alcohols, e.g., ethanol, or organic acids. The productobtained depends upon the microorganism utilized and the conditionsunder which the bioprocessing occurs. These steps can be performed, forexample, utilizing the existing equipment of the corn-based ethanolmanufacturing facility.

The mixing processes and equipment discussed herein may also be usedduring bioprocessing, if desired. Advantageously, the mixing systemsdescribed herein do not impart high shear to the liquid, and do notsignificantly raise the overall temperature of the liquid. As a result,the microorganisms used in bioprocessing are maintained in a viablecondition throughout the process. Mixing may enhance the reaction rateand improve the efficiency of the process.

Generally, fermentation utilizes various microorganisms. The sugarsolution produced by saccharification of lignocellulosic materials willgenerally contain xylose as well as glucose. It may be desirable toremove the xylose, e.g., by chromatography, as some commonly usedmicroorganisms (e.g., yeasts) do not act on xylose. The xylose may becollected and utilized in the manufacture of other products, e.g.,animal feeds and the sweetener Xylitol. The xylose may be removed priorto or after delivery of the sugar solution to the manufacturing facilitywhere fermentation will be performed.

The microorganism can be a natural microorganism or an engineeredmicroorganism, e.g., any of the microorganisms discussed in theMaterials section herein.

The optimum pH for yeast is from about pH 4 to 5, while the optimum pHfor Zymomonas is from about pH 5 to 6. Typical fermentation times areabout 24 to 96 hours with temperatures in the range of 26° C. to 40° C.,however thermophilic microorganisms prefer higher temperatures.

Carboxylic acid groups generally lower the pH of the fermentationsolution, tending to inhibit fermentation with some microorganisms, suchPichia stipitis. Accordingly, it is in some cases desirable to add baseand/or a buffer, before or during fermentation, to bring up the pH ofthe solution. For example, sodium hydroxide or lime can be added to thefermentation medium to elevate the pH of the medium to range that isoptimum for the microorganism utilized.

Fermentation is generally conducted in an aqueous growth medium, whichcan contain a nitrogen source or other nutrient source, e.g., urea,along with vitamins and trace minerals and metals. It is generallypreferable that the growth medium be sterile, or at least have a lowmicrobial load, e.g., bacterial count. Sterilization of the growthmedium may be accomplished in any desired manner. However, in preferredimplementations, sterilization is accomplished by irradiating the growthmedium or the individual components of the growth medium prior tomixing. The dosage of radiation is generally as low as possible whilestill obtaining adequate results, in order to minimize energyconsumption and resulting cost. For example, in many instances, thegrowth medium itself or components of the growth medium can be treatedwith a radiation dose of less than 5 Mrad, such as less than 4, 3, 2 or1 Mrad. In specific instances, the growth medium is treated with a doseof between about 1 and 3 Mrad.

In some embodiments, all or a portion of the fermentation process can beinterrupted before the low molecular weight sugar is completelyconverted to ethanol. The intermediate fermentation products includehigh concentrations of sugar and carbohydrates. These intermediatefermentation products can be used in preparation of food for human oranimal consumption. Additionally or alternatively, the intermediatefermentation products can be ground to a fine particle size in astainless-steel laboratory mill to produce a flour-like substance.

Mobile fermentors can be utilized, as described in U.S. Ser. No.12/374,549 filed Jan. 21, 2009, now Published International ApplicationNo. WO 2008/011598. Similarly, the saccharification equipment can bemobile. Further, saccharification and/or fermentation may be performedin part or entirely during transit.

Post-Processing

After fermentation, the resulting fluids can be distilled using, forexample, a “beer column” to separate ethanol and other alcohols from themajority of water and residual solids. The vapor exiting the beer columncan be, e.g., 35% by weight ethanol and can be fed to a rectificationcolumn. A mixture of nearly azeotropic (92.5%) ethanol and water fromthe rectification column can be purified to pure (99.5%) ethanol usingvapor-phase molecular sieves. The beer column bottoms can be sent to thefirst effect of a three-effect evaporator. The rectification columnreflux condenser can provide heat for this first effect. After the firsteffect, solids can be separated using a centrifuge and dried in a rotarydryer. A portion (25%) of the centrifuge effluent can be recycled tofermentation and the rest sent to the second and third evaporatoreffects. Most of the evaporator condensate can be returned to theprocess as fairly clean condensate with a small portion split off towaste water treatment to prevent build-up of low-boiling compounds.

Intermediates and Products

Using the processes described herein, the treated biomass can beconverted to one or more products, such as energy, fuels, foods andmaterials. Specific examples of products include, but are not limitedto, hydrogen, sugars (e.g., glucose, xylose, arabinose, mannose,galactose, fructose, disaccharides, oligosaccharides andpolysaccharides), alcohols (e.g., monohydric alcohols or dihydricalcohols, such as ethanol, n-propanol, isobutanol, sec-butanol,tert-butanol or n-butanol), hydrated or hydrous alcohols, e.g.,containing greater than 10%, 20%, 30% or even greater than 40% water,xylitol, biodiesel, organic acids, hydrocarbons (e.g., methane, ethane,propane, isobutene, pentane, n-hexane, biodiesel, bio-gasoline andmixtures thereof), co-products (e.g., proteins, such as cellulolyticproteins (enzymes) or single cell proteins), and mixtures of any ofthese in any combination or relative concentration, and optionally incombination with any additives, e.g., fuel additives. Other examplesinclude carboxylic acids, salts of a carboxylic acid, a mixture ofcarboxylic acids and salts of carboxylic acids and esters of carboxylicacids (e.g., methyl, ethyl and n-propyl esters), ketones (e.g.,acetone), aldehydes (e.g., acetaldehyde), alpha, beta unsaturated acids,such as acrylic acid and olefins, such as ethylene. Other alcohols andalcohol derivatives include propanol, propylene glycol, 1,4-butanediol,1,3-propanediol, sugar alcohols (e.g., erythritol, glycol, glycerol,sorbitol threitol, arabitol, ribitol, mannitol, dulcitol, fucitol,iditol, isomalt, maltitol, lactitol, xylitol and other polyols), methylor ethyl esters of any of these alcohols. Other products include methylacrylate, methylmethacrylate, lactic acid, citric acid, formic acid,acetic acid, propionic acid, butyric acid, succinic acid, valeric acid,caproic acid, 3-hydroxypropionic acid, palmitic acid, stearic acid,oxalic acid, malonic acid, glutaric acid, oleic acid, linoleic acid,glycolic acid, γ-hydroxybutyric acid, and mixture thereof, a salt of anyof these acids, or a mixture of any of the acids and their respectivesalts. a salt of any of the acids and a mixture of any of the acids andrespective salts.

Other intermediates and products, including food and pharmaceuticalproducts, are described in U.S. Ser. No. 12/417,900 filed Apr. 3, 2009,the full disclosure of which is hereby incorporated by reference herein.

OTHER EMBODIMENTS

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure.

In some implementations, the systems discussed herein, or components ofthese systems, may be portable, e.g., in the manner of the mobileprocessing equipment described in U.S. Ser. No. 12/374,549 filed Jun. 2,2009 and International Application No. WO 2008/011598, the fulldisclosures of which are incorporated herein by reference.

While tanks have been referred to herein, the process may take place inany type of vessel or container, including lagoons, pools, ponds and thelike. If the container in which mixing takes place is an in-groundstructure such as a lagoon, it may be lined. The container may becovered, e.g., if it is outdoors, or uncovered.

In an alternate embodiment, the dispersing system 134 can be omitted inthe systems shown in FIGS. 2A and 2B, and a pump can be used to drawliquid from the tank and deliver it through outlet pipe 137 to wet thefeedstock material, which is then dispersed by the mixing action of thejet mixer 144. In such implementations, the pump would preferably be alow shear pump, e.g., a positive displacement pump such as theprogressive cavity pumps available from SEEPEX and lobe pumps fromWaukesha. It is also preferred that the pump be capable of pumping highviscosity fluids, since the viscosity of the liquid will increase asmore feedstock is added.

While biomass feedstocks have been described herein, other feedstocksand mixtures of biomass feedstocks with other feedstocks may be used.For example, some implementations may utilize mixtures of biomassfeedstocks with hydrocarbon-containing feedstocks such as thosedisclosed in U.S. Ser. No. 13/293,985 filed Nov. 10, 2011, the fulldisclosure of which is incorporated by reference herein.

Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A wet milling system comprising a tank with oneor more jet heads and one or more wet mills disposed within the tank. 2.The system of claim 1 wherein the one or more wet mills comprise a headcomprising a rotor and a stator.
 3. The system of claim 2 wherein therotor and the stator include nesting rings of teeth.
 4. The system ofclaim 3 wherein the stator comprises two or more concentric rings ofteeth.
 5. The system of claim 2 wherein the clearance between the rotorand the stator is from about 0.01 to 0.25 inches (0.25 to 6.4 mm). 6.The system of claim 3 wherein the spacing between teeth in each ring ofteeth is from about 0.1 to 0.3 inch (2.5 to 7.6 mm).
 7. A wet millingsystem comprising one or more jet heads and one or more wet millingheads in a tank comprising fluid having biomass dispersed therein. 8.The system of claim 7 wherein the biomass is selected from the groupconsisting of wood, particle board, sawdust, agricultural waste, sewage,silage, grasses, rice hulls, bagasse, cotton, jute, hemp, flax, bamboo,sisal, abaca, straw, wheat straw, corn cobs, corn stover, switchgrass,alfalfa, hay, coconut hair, seaweed, algae, and mixtures thereof.
 9. Thesystem of claim 8 wherein the agricultural waste is selected from thegroup consisting of: rice hulls, bagasse, straw, corn stover and coconuthair.
 10. The system of claim 8 wherein the silage is alfalfa.
 11. Thesystem of claim 7 wherein the biomass comprises a lignocellulosicmaterial.
 12. The system of claim 11 wherein the recalcitrance of thelignocellulosic material has been reduced by irradiating the biomass.13. The system of claim 12 wherein irradiating comprises exposing thebiomass to an electron beam.
 14. The system of claim 7 wherein the oneor more wet milling heads comprise a rotor and a stator.
 15. The systemof claim 14 wherein the rotor and the stator include nesting rings ofteeth.
 16. The system of claim 15 wherein the stator comprises two ormore concentric rings of teeth.
 17. The method of claim 14 wherein theclearance between the rotor and the stator is from about 0.01 to 0.25inches (0.25 to 6.4 mm).
 18. The method of claim 15 wherein the spacingbetween teeth in each ring of teeth is from about 0.1 to 0.3 inch (2.5to 7.6 mm).